Atmospheric CO2 and oceanic acidity

While the impact of increasing concentrations of carbon dioxide in the atmosphere is widely discussed, I have seen rather less attention paid to important chemical changes it causes in the oceans. In particular, that includes how increased atmospheric concentrations of CO2 cause the ocean to become more acidic. (BBC article) Some predictions hold that oceanic pH will fall by 0.4 in the next ninety years or so. Remember that pH is a logarithmic scale: a solution with a pH of 6 is ten times more acidic than one with a pH of 7.

One important consequence of this lowering of pH is that it decreases the amount of calcium carbonate (chalk) that is in solution in the seawater. Calcium carbonate is the primary material from which the hard structures of many marine organisms are made: from shells to coral reefs.

Increased oceanic acidity begins at the poles and progresses towards the equator, where most of the world’s coral reefs – and marine biomass in general – are located. Intuitively, the difficulty of grasping the knock-on effects of such a chemical transition is obvious. Oceanic acidity is likely to affect other biological systems, including the overall distribution of species within and between ecosystems. It is a further reminder of the unpredictable consequences that will result from increasing CO2 concentrations: concentrations that will be double their pre-industrial levels within 45 years, at present rates of growth.

“Increasing atmospheric carbon dioxide concentrations lead to increasing acidification of the ocean. Projections based on SRES scenarios give reductions in average global surface ocean pH of between 0.14 and 0.35 units over the 21st century, adding to the present decrease of 0.1 units since pre-industrial times.”

The uptake of anthropogenic carbon since 1750 has led to the ocean becoming more acidic with an average decrease in pH of 0.1 units. Increasing atmospheric CO2 concentrations lead to further acidification. Projections based on SRES scenarios give a reduction in average global surface ocean pH of between 0.14 and 0.35 units over the 21st century. While the effects of observed ocean acidification on the marine biosphere are as yet undocumented, the progressive acidification of oceans is expected to have negative impacts on marine shellforming organisms (e.g. corals) and their dependent species.

The world’s oceans are becoming acidic at a faster rate than at any time in the last 55m years, threatening disaster for marine life and food supplies across the globe, delegates at the UN climate conference in Copenhagen have been warned.

A report by more than 100 of Europe’s leading marine scientists, released at the climate talks this morning, states that the seas are absorbing dangerous levels of carbon dioxide as a direct result of human activity. This is already affecting marine species, for example by interfering with whale navigation and depleting planktonic species at the base of the food chain.

Ocean acidification – the facts says that acidity in the seas has increased 30% since the start of the industrial revolution. Many of the effects of this acidification are already irreversible and are expected to accelerate, according to the scientists.

The study, which is a massive review of existing scientific studies, warns that if CO2 emissions continue unchecked many key parts of the marine environment – particularly coral reefs and the algae and plankton which are essential for fish such as herring and salmon – will be “severely affected” by 2050, leading to the extinction of some species.

New research proves, via direct measurements, that man-made carbon dioxide in the atmosphere is causing declines in ocean pH (ocean acidification) across the Pacific and detectable as far down as a half-mile.

Researchers compared over 1500 water samples collected from Hawai’i to Alaska with samples collected in 1991 over the same area. The results: the surface layer is nearly 6 percent more acidic than it was 15 years ago. Below 2400 ft, the waters appear unchanged … for now.